Environmental control kit for sealed cabinets

ABSTRACT

A heat exchanger kit useful for installation in an existing electrical equipment cabinet, said cabinet having an enclosure adapted to contain heat-generating electrical equipment, at least one access opening, and a door providing a closure for said access opening; the kit including a replacement door for the cabinet and mounted thereon, a louvered shroud, creating an enclosure within said shroud defined by the replacement door and the shroud, an air-to-air heat exchanger mounted on the exterior of the replacement door, and supported thereby, for removing heat from the interior of the cabinet while maintaining the substantially closed environment within the cabinet. The heat exchanger has a first air flow path for air drawn from the exterior of said cabinet and a second air flow path from the interior of said cabinet, where the first and second air flow paths are perpendicular to one another and are substantially isolated from each other; and further including at least one fan for circulating air through at least one of a first and a second air flow paths.

FIELD OF THE INVENTION

[0001] The present invention relates to a kit for use in an electrical equipment cabinet to provide an environmental control system to exchange air to remove heat or provide active cooling for the cabinet interior. More specifically, the invention relates to a ready-to-mount kit which can be installed into an already in-use cabinet, employing a modular, cross-flow heat exchanger or air conditioner that is mounted on the exterior of the cabinet door.

BACKGROUND OF THE INVENTION

[0002] Outdoor electrical equipment cabinets are often used to protect sensitive electronic equipment such as telecommunications equipment from tampering, vandalism and adverse environmental conditions. The electronic components housed in the cabinets produce heat when operating. Therefore, a heat exchanger or other cooling system is required to remove the heat from the cabinets. As the electronic components become smaller and operate at higher power densities, cabinets need to dissipate heat more efficiently.

[0003] One example of a conventional outdoor electrical equipment cabinet is disclosed in U.S. Pat. No. 4,535,386 (Frey, Jr. et al.). This cabinet employs a heat exchanger to dissipate internally generated heat. The heat exchanger exchanges heat between the air in the cabinet and the ambient air outside the cabinet, without allowing the interior and ambient air to mix. In this way, a substantially closed or sealed environment can be maintained within the cabinet, while still allowing for adequate heat dissipation. The heat exchanger is located in the main portion of the cabinet, in proximity to the electronics requiring cooling. However, the presence of the heat exchanger in the cabinet can interfere with the cables used to interconnect the various electronic components, making the routing of these cables somewhat more difficult. Also, since the heat exchanger occupies a significant amount of space, the cabinet must usually be made larger to accommodate it.

[0004] U.S. Pat. No. 5,467,250 (Howard et al.) discloses an electrical equipment cabinet that employs a door-mounted heat exchanger so that the heat exchanger does not occupy internal space required for the electrical equipment while maintaining a closed or sealed environment within the cabinet. An arrangement of ducts and vents is used to force interior and exterior air through channels in the heat exchanger using powered fans mounted within the main portion of the cabinet. The mounting of the heat exchanger on or within the door of the cabinet makes more efficient use of the space available within the cabinet.

[0005] However, the heat exchanger employed in Howard et al. is a parallel flow heat exchanger in which the channels conducting interior air are parallel to the channels conducting exterior air. The housing in which the heat exchanger is located contains two sets of interdigitated vents for conducting internal and external air through the heat exchanger. In order to ensure that the flow of exterior air remains isolated from the flow of interior air, each set of interdigitated vents must be in precise registration with either the channels conducting interior air or the channels conducting exterior air. One problem with this arrangement is that the manufacturing and assembly is difficult because of the precise tolerances involved.

[0006] Other problems and service issues associated with the above types of air-to-air fan-forced heat exchanger systems installed on cabinets remotely located from the cabinet owner's office include fan failures, core clogging, etc. If the heat exchanger system has only one air moving device (e.g., fan or blower) on each flow circuit, then failure of a single fan effectively kills the heat exchange function (near 100% performance reduction). If multiple fans are employed on each flow circuit, failure of one fan can create a open air outlet which allows the some of the airflow delivered by the active fan to backflow through the dead fan rather than flowing through the core, resulting in useless re-circulatory airflow which lowers the overall performance of the heat exchanger system below that which would be achieved if the second fan were not present.

[0007] Heat exchanger core clogging/fouling is caused by dust and grime present in the outdoor air. Clogging can reduce the performance of the heat exchanger system over time by clogging the air passages through the heat exchanger core, reducing airflow. The core's performance is also reduced when dust or grime coats the core's heat transfer surface, increasing overall thermal resistance.

[0008] If an intake filter is used to mitigate the previous problem, the filter will eventually get clogged with dust and dirt such that intake airflow will be reduced, lowering the overall performance of the heat exchanger system. Therefore, filters typically require frequent replacement.

[0009] Because the cabinets are located remotely, frequent maintenance visits are both inconvenient and expensive. If the filter panel is external to the cabinet, it is subject to tampering by vandals or unauthorized personnel. If access requires entering the cabinet where the sensitive/expensive/hazardous electronics are located, the task must be performed by highly trained personnel, which adds to the maintenance cost.

[0010] Further, the remote cabinets may be located in residential areas, where noise emission is restricted. As the volume of outside air moved by the heat exchanger system increases, the noise level inevitably rises. Therefore it is advantageous to maximize the heat dissipation realized by a given amount of ambient airflow.

[0011] System replacement/upgrading capability is crucial. The equipment cabinet's cooling requirements may change over time as the electronics are upgraded and/or replaced. This requires that any cooling solution also be upgradeable. It may be necessary to retrofit the cooling solution onto existing cabinets in the field.

[0012] Outdoor equipment cabinets represent a substantial investment for telecommunications companies; and thousands of such cabinets without any environmental control system already are present in both residential and commercial settings. As subscribers upgrade services it is not feasible to simply replace all the traditional non-environmentally controlled cabinets with new cabinets. The cost is prohibitive, labor time extensive, and service would be interrupted during the replacement time period. For this reason, there is a need for a retrofit solution that can be added to traditional cabinets in place to enable them to provide the necessary environmental control for the new upgraded electronic equipment. The combination of a large filter and a high efficiency heat exchanger that is mounted inside a shroud significantly reduces the amount of maintenance, i.e., clogged filter changes required, as well as allowing filter replacement to be done by lesser technical personnel as they need not be qualified to access the electronic equipment. These and other needs are met by the present invention, as hereinafter described.

SUMMARY OF THE INVENTION

[0013] The present invention provides an environmental control kit for use in electrical equipment cabinets containing heat-generating electrical equipment.

[0014] In another aspect, the invention provides an electrical equipment cabinet comprising an add-on environmental control system kit that has been installed in the cabinet.

[0015] More specifically, the environmental control kit includes an air-to-air cross-flow heat exchanger that can be mounted on and supported by the door of an electrical equipment cabinet, and which operates to remove heat from the interior of the cabinet while maintaining the substantially closed environment therein. The kit includes a replacement door for the cabinet having the appropriate orifices drilled therein. For practical purposes, the heat exchanger kit is assembled on the replacement door prior to delivery to the field. The heat exchanger defines a first air flow path for air drawn from the exterior of the cabinet and a second air flow path for air drawn from the interior of the cabinet. The first and second air flow paths are approximately perpendicular to, and substantially isolated from, one another. A fan element for each flow path is also mounted in an enclosed space created between the door and the louvered shroud for circulating air through one of the first and second air flow paths.

[0016] In accordance with another aspect of the invention, the kit is mounted on the exterior of the replacement door and has a shroud or housing fit over the heat exchanger, thus creating an enclosed region that extends outward from the former exterior of the door so that the electronic equipment enclosure is separate from and does not need to be accessed to access the heat exchanger enclosure.

[0017] In accordance with one aspect of the invention, the fan element for each flow path includes a pair of fans. In one embodiment, the fans may be located adjacent to one another. In a highly preferred embodiment, a baffle is located between the pair of fans for dividing the original flow path into two parallel air flow paths that are substantially isolated from one another.

[0018] In accordance with another aspect of the invention, the cabinet also includes upper and lower air flow plenums, which are mounted to an interior surface of the door. The cross-flow heat exchanger element is supported between the air flow plenums in a removably engagable manner.

[0019] In accordance with yet another aspect of the invention, the replacement door includes first and second external air vents conducting external air through one of the air flow paths.

[0020] As used herein, these terms have the following meanings.

[0021] 1. The term “kit” and “ready-to-mount kit” are synonymous and refer to a heat exchanger, blower therefore, shroud therefore, a replacement cabinet door, and all necessary accessory and mounting equipment to mount the exchanger kit onto an outdoor telecommunications cabinet. The use of the term “kit” does not necessarily mean that assembly of the exchanger itself, or mounting of the exchanger onto the replacement door by the customer is required.

[0022] 2. The term “core plenum” means a cover for the core.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a perspective view of an outdoor electrical cabinet incorporating a door-mounted, air-to-air heat exchanger in accordance with the present invention.

[0024]FIG. 2 is a perspective view showing the heat exchanger door kit with the hinged louvered shroud open, revealing enclosed space therein, the core plenum and the external intake blower assembly.

[0025]FIG. 3 shows the heat exchanger core plenum removed, revealing the respective positions of the removable heat exchanger core, the internal intake blower assembly, and the internal vent.

[0026]FIG. 4 is a perspective view of the door and heat exchanger system from the cabinet's interior.

[0027]FIG. 5 is a perspective view of all basic parts and assemblies of the heat exchanger, viewed from the cabinet's interior (door hidden). These parts all bolt onto the exterior door surface to form a complete heat exchanger system.

[0028]FIG. 6 is a perspective view of the external blower assembly.

[0029]FIG. 7 is a perspective view of the internal blower assembly.

[0030]FIG. 8 is a perspective view of a cross-flow heat exchanger core.

DETAILED DESCRIPTION OF THE INVENTION

[0031]FIG. 1 illustrates an outdoor electrical equipment cabinet 100 incorporating a door-mounted air-to-air heat exchanger kit, including a louvered shroud and a replacement door for the cabinet in accordance with the present invention. The cabinet has an original door, which is replaced by replacement door 101. The heat exchanger is mounted to the exterior of the replacement door 101; the kit further includes a hinged, louvered shroud 102 mounted over the heat exchanger. The cabinet itself contains a number of equipment racks or channel banks in an electronic equipment enclosure (not shown), inside the cabinet. The shroud 102 has a large louvered panel including louvers 103 visible from the exterior of the cabinet. The large louvered panel efficiently draws in air from the outside environment.

[0032]FIG. 2 shows a perspective view of the door with the heat exchanger kit installed, when the shroud is open. The hinged shroud 102 forms an enclosed space in which an inner housing 202 is located. The louvered shroud 102 includes inflow vents and outflow vents. The inner housing, which contains heat exchanger 202, includes the heat exchanger core 203, and external blower assembly 204. The hinged shroud 102 has large intake and exhaust louvers 201, and holds an intake dust filter 205, which filters the incoming air to prevent dust from contaminating and clogging the core 203. The hinged shroud 102 permits the filter 205 to be accessed and replaced without the need to open the door to the electronics enclosure. This permits personnel who are not electronic equipment specialists to service the filters. The blower assembly 204 has circular intakes 206 oriented at about a 65° angle to the intake wall 207 of the hinged louvered shroud 102, rather than being parallel. This reduces direct exposure of the external blowers to windblown rain and also hinders blower motor acoustic noise from escaping the shroud. This noise reduction can be further enhanced by providing a sound and vibration dampening film as a liner (not shown) on the shroud 102.

[0033] The add-on heat exchanger, including replacement door 101 and louvered shroud 102, is mounted so that the enclosed space of the door/heat exchanger unit extends outward from the cabinet and is separate and apart from the cabinet interior or enclosure, where the electrical/electronic equipment is located. This arrangement maximizes the space within the cabinet interior reserved for electrical equipment, and as noted, is advantageous because the heat exchanger can be serviced without accessing the cabinet interior.

[0034] In FIG. 3, the core plenum has been removed, revealing the removable heat exchanger core 301, the internal blower assembly 302 and the internal grill 303. Use of two blowers with a separating baffle provides operational redundancy.

[0035]FIG. 4 is a view of the door and heat exchanger from the interior of the door. The internal blower assembly 401 and the internal grill 402 are visible from within the electronic compartment, but they do not protrude into the compartment, thus maximizing the room inside the cabinet for electronic equipment.

[0036]FIG. 5 shows all the interior parts and the subassemblies of the heat exchanger. These parts are all typically pre-mounted onto the replacement door's exterior surface to form a complete heat exchanger assembly. Baffle 501 separates the flow paths of the two external blowers 502. Similarly, the interior flow baffle 503 separates the flow paths of the two internal blowers. Having two internal blowers and two external blowers in the kit provides operational redundancy so that if a single blower, either external or internal, fails, the remaining blower continues to operate, protecting the electronic equipment compartment from a rapid increase in air temperature which could damage the sensitive equipment and disrupt service to subscribers.

[0037]FIG. 6 shows the external blower assembly 600. L-shaped foam blocks 601 help seal the blower paths when the assembly is mounted onto the door.

[0038]FIG. 7 shows the internal blower assembly. The baffle 701 divides the two blowers 702, the operation of which is controlled by the controller card 703.

[0039]FIG. 8 shows the construction of a bonded-aluminum single-pass cross-flow heat exchanger core 800, which may be used in the present invention. The core has finned channels 802 and 803 in arranged in alternating perpendicular layers. Each layer includes a multiplicity of channels. When mounted on the door, three layers form the internal airflow path 802 and four layers form the external airflow path 803. The extra layer for the external flow path results in less flow impedance. This helps to offset the extra flow impedance of the external flow filter and louvered shroud.

[0040] The heat exchanger 202 is situated in the plenums so that the inflow vents of the louvered shroud 102 are aligned with the inflow openings of the horizontal channels 803 of the heat exchanger core 800. Likewise, the outflow vents of the louvered shroud 102 are aligned with the outflow openings of the horizontal channels 803 of the heat exchanger. Accordingly, the horizontal channels are exposed to air outside the sealed cabinet.

[0041] In operation, air exterior to the cabinet 100 is drawn through the intake vents 103 of the louvered shroud 102 so that external air flows into the horizontal channels 803. The air exits the horizontal channels 803 and flows through output vents of the louvered shroud shell 102 to exit the cabinet 100.

[0042] Internal air, which contains heat generated by the electrical equipment within the cabinet 100, is drawn into the intake openings of the vertical channels 802 of the heat exchanger core 800. The internal air is conducted through the vertical channels 802 and exits the heat exchanger via the output openings of the vertical channels 802. In this way the heat contained in the internal air is transferred to the outside air flowing through the horizontal channels 803 of the heat exchanger element 800 by the combination of forced convection and conductive heat transfer.

[0043] From the foregoing description, it will be appreciated that a continuous re-circulating flow of interior air is maintained through the equipment located in the cabinet 100, and the vertical channels 802 of the heat exchanger core 800. At the same time, a separate flow or circuit of outside air is drawn in through the vents 103 of the louvered shroud 102, forced through the heat exchanger element 800 by means of the fans, and then passes out of the cabinet 100 through the vents 103 in outer louvered shroud 102. Since the internal and external flow circuits are isolated from each other and do not mix, the environment within the cabinet 100 remains sealed while heat is removed from the interior of the cabinet by means of the heat exchanger element 800.

[0044] To ensure that the outside circuit of air does not mix with the internal circuit of air, the core plenum 202 may be provided with a sealant that prevents leakage of air between the terminal ends of the horizontal and vertical channels. The sealant, which may be a silicon compound, for example, should be provided along the lines where the plenums, heat exchanger element and panel 207 meet.

[0045] The kit of the invention with its louvered shroud including a large louvered panel and large filter combined with a high efficiency cross-flow heat exchanger significantly reduces the number of maintenance visits required to service the heat exchanger. This reduces costs for the telecommunications providers who have huge numbers of such cabinets, and allows the heat-exchanger maintenance to be provided by personnel not qualified to access or service the complex electronic equipment inside the cabinet.

[0046] If more environmental control is desired, the heat exchanger core described herein may be replaced by a compressor driven heat pump having an evaporator and a condenser.

[0047] The preceding description of the present invention is merely illustrative, and is not intended to be limiting. Therefore, the scope of the present invention should be construed solely by reference to the appended claims. 

What is claimed is:
 1. A heat exchanger kit useful for installation in an existing electrical equipment cabinet, said cabinet having an electronic equipment compartment adapted to contain heat-generating electrical equipment, at least one access opening, and a door providing a closure for said access opening, said kit comprising a replacement door having interior and exterior surfaces for said cabinet having mounted thereon: a shroud creating an enclosure within said shroud defined by said replacement door and said shroud, an air-to-air heat exchanger mounted on the exterior surface of the replacement door, and being supported thereby, for removing heat from the interior of said cabinet while maintaining said substantially closed environment within said cabinet, said heat exchanger having a first air flow path for air drawn from the exterior of said cabinet and a having a second air flow path from the interior of said cabinet, said first and second air flow paths being perpendicular to one another and being substantially isolated from each other; and at least one fan for circulating air through each of said first and said second air flow path.
 2. The heat exchanger kit of claim 1, wherein said fan comprises a pair of fans to be located adjacent to one another, and further comprises a baffle located between said pair of fans for dividing the flow path into two parallel air flow paths substantially isolated from one another.
 3. The heat exchanger kit of claim 1, further comprising upper and lower air flow plenums to be mounted to an exterior surface of said replacement door, said heat exchanger being supported between said air flow plenums.
 4. The heat exchanger kit of claim 2, wherein said pair of fans circulate air through the first air flow path.
 5. The heat exchanger kit of claim 2, wherein said pair of fans circulate air through the second air flow path.
 6. The heat exchanger kit of claim 1, wherein said fan is mounted on said exterior of said replacement door to perform air intake.
 7. The heat exchanger kit of claim 1, wherein said fan is mounted on said interior surface of said replacement door to perform air outflow.
 8. The heat exchanger kit of claim 2, wherein said pair of fans are mounted on said exterior of said replacement door to perform air intake.
 9. The heat exchanger kit of claim 2, wherein said pair of fans are mounted on said interior surface of said replacement door to perform air outflow.
 10. The heat exchanger kit of claim 1, wherein said heat exchanger enclosure extends outward from the replacement door to the louvered shroud, such that said enclosure does not protrude into said electronic equipment compartment.
 11. A heat pump kit useful for installation in an existing electrical equipment cabinet, said cabinet having an electronic equipment compartment adapted to contain heat-generating electrical equipment, at least one access opening, and a door providing a closure for said access opening, said kit comprising a replacement door for said cabinet having mounted thereon: a shroud creating an enclosure within said shroud defined by said replacement door and said shroud, a compressor driven heat pump mounted on the exterior of the replacement door, and being supported thereby, for removing heat from the interior of said cabinet while maintaining said substantially closed environment within said cabinet, said heat pump having evaporator and condenser sections, each section having at least one fan for circulating air through a flow path.
 12. An outdoor telecommunications cabinet having the heat exchanger kit of claim 1 mounted on an access opening thereto.
 13. An outdoor telecommunications cabinet having a plurality of access openings, at least one of said access openings having the heat exchanger kit of claim 1 mounted thereon.
 14. An outdoor telecommunications cabinet having a plurality of access openings, each access opening having the heat exchanger kit of claim 1 mounted thereon.
 15. An outdoor telecommunications cabinet having the heat pump kit of claim 11 mounted on an access opening thereto. 